This invention relates to a back door structure mounted so as to be capable of opening the rear of an automobile body.
Conventionally, the back door of an automotive vehicle such as a hatch back-, van- or station wagon-type automobile includes a back door body formed to include an opening for a window in the upper portion thereof and provided on the rear of the automobile body so as to be capable of opening the same. A sheet of window glass is mounted in the window opening and a recess for receiving the vehicle license plate or the like is formed on the outer side of the back door body beneath the window.
The back door body usually is composed of two panel members, namely an outer panel and an inner panel. From the standpoint of design considerations, the outer panel, which forms the outer surface of the back door body, should readily lend itself to any change in shape or styling. Various art has heretofore been proposed for this purpose, an example of which is disclosed in the specification of Japanese Utility Model Application Laid-Open (KOKAI) No. 56-31917. In the art disclosed, the outer panel is divided into at least upper and lower portions. These upper and lower portions are joined in a state where an edge portion of one overlaps a corresponding edge portion of the other. Thus, the conventional back door body is of a so-called "divided" structure. This divided structure is adopted instead of one in which the outer panel is constituted by a single panel member because the latter cannot be freely modified in shape and styling due to machining considerations.
This conventional divided structure has the following problems relating to the location at which the outer panel is divided into the upper and lower panels:
(1) If the outer panel is divided through the portion of the window opening formed in the upper panel, the upper panel will have insufficient rigidity before it is joined to the lower panel. This means that it is necessary to enlarge the thickness of the plate forming the upper panel.
(2) The portion where the two panels are joined together forms a portion of the window glass fixing surface. This makes it necessary to join the two panels together with a high accuracy. If the joint is insufficiently accurate, a sealer covering the joint will crack and allow water to leak into the car body.
(3) If the outer panel is divided below the window opening, on the other hand, the joint will be exposed to external view and will require to be covered by the mounting of finisher or the like. This increases the number of assembly steps and component parts and results in higher production cost.